Pancreatic Cancer

•  Development of Pancreatic Cancer

  • Development of ductal adenocarcinoma is a sequential process beginning with normal ductal epithelial cells. Neoplasia deriving from these cells start from intraductal proliferative lesions, ending in invasive carcinomas. The process is analogous to that observed with other cancers arising from ductal epithelium, including prostate cancer and breast ductal carcinoma. Pancreatic intraepithelial neoplasm (PanIN) refers to intraductal proliferative epithelial lesions that are graded as 1A, 1B, 2 and 3 representing progression along a dysplastic path.⁹

  • Normal Ductal and Ductular Pancreatic Epithelium (right) ¹⁹

    In the normal case ductal and ductular epithelial cells is described as cuboidal to low-columnar epithelial with amphophilic cytoplasm. What is not seen includes mucinous cytoplasm, nuclear crowding and atypia.19 (amphophilic refers to staining with either basic or acid dyes) [just as an example consider this picture (below) of an immunoblastic lymphoma immunoblast (center arrow); observed as a large, red, central nucleolus, fairly clear chromatin and bluish-red (amphophilic) cytoplasm.20

  •  

    Squamous Metaplasia ¹⁹

    Squamous metaplasia represents a transitional morphology characterized by replacement of normal cuboidal ductal epithelium by transitional epithelium without atypia or by mature squamous epithelium.

  •  

    PanIN-1A (Pancreatic Intraepithelial Neoplasia 1-A) ¹⁹

    PanIN-1A is an abbreviation for pancreatic intraepithelial neoplasia 1-A. These lesions are described as flat, composed of tall columnar cells with nuclei located basally and significant amounts of supranuclear mucin (mucin refers to a family of heavily glycosylated proteins). Nuclei tend to be small and round to oval. Oval nuclei are typically oriented perpendicular to the basement membrane. Because of histological uncertainty, the neoplastic character of many examples of PanIN-1A  remains unestablished.

  •  

    PanIN-1B (Pancreatic Intraepithelial Neoplasia 1-B) ¹⁹

    PanIN-1B exhibit a pseudostratified architecture (papillary or micropapillary in appearance). These epithelial lesions are otherwise identical to PanIN-1A.

     

    PanIN-2 (Pancreatic Intraepithelial Neoplasia 2) ¹⁹

    PanIN-2 (pancreatic intraepithelial neoplasia 2) are mucinous lesions appearing either flat or papillary. Nuclear abnormalities may include some polarity loss, nuclear crowding, enlarged nuclei, pseudo-stratification and hyperchromatism. With hyperchromatism the nuclei will tend to stain more intensely than normal. More nuclear abnormalities are observed in PanIN-3. Mitoses occur rarely.

  •  

    PanIN-3 (Pancreatic Intraepithelial Neoplasia 3) ¹⁹

    PanIN-3 (pancreatic intraepithelial neoplasia 3) are usually papillary or micropapillary, rarely flat. Suggestive of the diagnosis of PanIN-3 include "true cribriforming, budding off of small clusters of epithelial cells into the lumen as well as luminal necrosis." These lesions show a loss of nuclear polarity, dystrophic goblet cells ("goblet cells with nuclei oriented towards the lumen and mucinous cytoplasm oriented towards the basement membrane") as well as mitoses (sometimes abnormal), along with nuclear irregularities with prominent nucleoli.

  •  

    Progression Model for Ductal Pancreatic Adenocarcinoma²¹

     

  • There are several reasons supporting the idea that PanINs (Pancreatic Intraepithelial Neoplasias) precede infiltrating ductal pancreatic adenocarcinomas. For example, PanINs are typically found in pancreata with infiltrating cancer. Moreover, PanINs (higher-grade) are more common in pancreata in patients diagnosed with pancreatic cancer than in patients without the disease. Also, some PanINs are observed directly to progress to infiltrating cancer over time. Probably most notably, however, is that PanINs display many genetic changes associated with infiltrating adenocarcinomas. Examples of these changes include activating point mutations in codon 12 of the K-ras gene which is common in infiltrating adenocarcinomas. Tumor suppressor gene mutations have also been described in PanINs including p16, p53, BRCA2, and DPC4.¹¹

  • Staging:

    • Pancreatic cancer staging consists of three primary divisions: (1) resectable, (2) locally advanced and (3) metastatic. Treatment options as well as survival estimates vary in accord with these groups. Staging descriptions have been provided by the American Joint Committee on Cancer: Cancer Staging for Exocrine Pancreas.²²

      • Considering first the primary tumor (T)-note the following categories:

        • TX: "Primary tumor cannot be assessed"

          T0: "No evidence of primary tumor"

          Tis: "Carcinoma in situ"

          T1: "Tumor limited to pancreas, 2 cm or less and greatest dimension"

          T2: "Tumor limited to pancreas, more than 2 cm and greatest dimension"

          T3: "Tumor extends beyond the pancreas that without involvement of the celiac axis or the superior mesenteric artery"

          T4: "Tumor involves the celiac axis or the superior mesenteric artery (unresectable primary tumor)

      • Next, pathology of regional lymph nodes (N) is considered:

        • NX: "Regional lymph nodes cannot be assessed"

          N0: "No regional lymph node metastasis"

          N1: "Regional lymph node metastases"

      • The question of distant metastatic disease is considered:

        • MX: "Distant metastases cannot be assessed"

          M0: "No distant metastases"

          M1: "Distant metastases"

    • These descriptions are in accord with the sixth edition of the American Joint Committee on Cancer (AJCC) staging system.²² 

    • Cancer Staging for Exocrine Pancreas (AJCC)

      Stage 0	Tis	N0	M0
      Stage IA	T1	N0	M0
      Stage IB	T2	N0	M0
      Stage IIA	T3	N0	M0
      Stage IIB	T1	N1	M0
      	T2	N1	M0
      	T3	N1	M0
      Stage III	T4	Any N	M0
      Stage IV	Any T	Any N	M1

    • Pathology and Staging Issues:

      • Background: pancreatic acinar cells account for about 80% of both the cell number and length volume; islet cell clusters account for about 1-2%. The pancreatic ductal system is principally comprised of single-layered, cuboidal epithelial cells which constitute about 10-15% of gland structure. With cancer, the histological features change notably: atrophic acini with dense collagenous stroma are apparent, although islet cell clusters remain well demarcated. The number of pancreatic ducts may increase to some extent. The associated photomicrograph illustrates these differences between normal pancreas and adenocarcinoma.

        • Photomicrograph of ductal adenocarcinoma compared to normal pancreas

          "Photomicrograph ductal adenocarcinoma the pancreas with well-preserved islet cells in pancreatic architecture above and infiltrating tumor was poorly formed glandular structures below."26

      • Histological identification factors: these considerations and factors are central for the diagnosis of ductal adenocarcinoma based on histological findings and include²⁶:

        • (1) nuclear and cellular pleomorphism. Pleomorphism is a cytological term used to describe variation in shape and size of cells and/or nuclei. Obviously, in this case both cellular form and nuclear form are important. Probably the most characteristic histologic example of pleomorphic pancreatic carcinoma is the mononuclear tumor giant cell. The cell tends to be a large, ovoid to irregular cell. The size varies from about 20 µm to 60 µm. The cell nucleus may be round to angulated or irregular, sometimes exhibiting bizarre shapes with multilobular character²⁷ . Inclusion of this cancer type here is only to illustrate pleomorphism. Pleomorphic pancreatic carcinoma, however, is comparable to pancreatic adenocarcinoma in many clinical features, although it is more likely to develop in the body and tail of the pancreas. This pancreatic tumor predisposes to metastases with hematogenous spread more common than that noted with pancreatic adenocarcinoma-the median survival may even be worse²⁷ .

          • Mononuclear Tumor Cells: Note eccentric nuclei and homogeneous eosinophilic cytoplasm²⁷

        • (2) identification of mitoses²⁶

        • (3) ductal epithelium discontinuity²⁶

        • (4) indications of lymphatic, vasicular or perineural tumor invasion²⁶

        • Pancreatic adenocarcinomas are most likely to occur in the head of the pancreas. However, other benign as well as malignant tumors that also occur are more likely to be distributed evenly in the body and tail of the pancreas. These other tumors are typically less aggressive than pancreatic adenocarcinomas and may have a better clinical outcome. Examples of these other lesions include pancreatic endocrine tumors, acinar cell carcinoma and cystadenocarcinomas. Nonpancreatic tumors of the distal bile duct, duodenum, and ampulla of Vater constitute about 33% of pancreatic resectable tumors localized in the pancreatic head. As noted earlier these tumors tend to be less aggressive than adenocarcinomas and are associated with a five-year disease-free survival rates from 30% to 50%.⁴ [The ampulla of Vater is an enlargement of ducks from both the liver and pancreas at the point where they enter the small intestine. Both hepatic bile and pancreatic secretions passed through the ampulla of Vater]

        • The importance of histologic tumor assessment is that the other tumor types are not readily distinguished from pancreatic adenocarcinoma based on radiological imaging studies, endoscopy, or even needle cytological assessment.

          • A primary tumor of the pancreas may be mimicked by a metastatic lesion. A clear cell renal carcinoma with metastatic spread to the ampullary region might appear, based on imaging, to be a primary pancreatic carcinoma.⁴

        • The aggressiveness assigned to pancreatic adenocarcinomas is reflected in metastatic spread. Patient to patient metastatic spread is often similar and includes local tumor invasion into surrounding structures. One example would be the encasement of the superior mesenteric or portal vein and the superior mesenteric artery-factors which may preclude surgical resection. Regional lymphatic spread is also frequently observed as is hepatic metastatic disease promoted through the portal vein. In advanced disease spread to peritoneal surfaces and lung is also observed.⁴  

        • CT Image of tumor within the pancreatic head²⁶

          "CT image of tumor within the pancreatic head. Note the stent in the bile duct and the subtle low-density mass within the head. The superior mesenteric artery (SMA) has a fat plane completely surrounding it. This defines a potentially resectable tumor."26

        • Histological classification of primary pancreatic exocrine tumors²⁶

          • Malignant: ductal adenocarcinoma, mucinous cystadenocarcinoma, acinar carcinoma, unclassified large cell carcinoma, small cell carcinoma, and pancreaticoblastoma.

          • Benign: serous cystadenoma

          • Uncertain, variable malignant potentiality: mucinous cystadenoma, intraductal papillary mucinous tumor

          • Papillary cystic neoplasm

        • In reference to the "staging" table above, pathologic staging is defined by the extent of tumor presence at local and distant sites. For example, stage I tumors are contained within the pancreas. Stage II tumors are locally invasive but do not involve the celiac or superior mesenteric artery. Stage II disease may involve regional lymph nodes, however. The importance of staging is reflected in the fact that stage I and II disease might be potentially resectable with an intention of cure. Stage III disease, by contrast, involves the celiac or superior mesenteric arteries; whereas, stage IV disease is characterized by distant metastatic spread. Patients with these more advanced stages are not generally viewed as candidates for potentially curative surgical interventions.

           

      • Pancreatic Adenocarcinoma: Gross Image²⁸

        "This section is taken through an adenocarcinoma of the head of the pancreas.  The lesion is a firm, tan-white mass that effaces the normal lobular architecture of the pancreas.   Although this carcinoma is only about 2.5 cm in diameter, it has already  invaded into the wall of the duodenum (large arrow) and metastasized to regional lymph nodes (small arrows)." attribution:  Gastrointestinal Pathology for Medical II Students, VCU Department of Pathology, http://www.pathology.vcu.edu/education/gi/lab1.c.html

         

      • Pancreatic Adenocarcinoma: Low-Power Histologic Slide²⁸

        "This low power view shows a moderately differentiated adenocarcinoma.  Irregularly shaped malignant glands are embedded in chronically inflamed fibrous tissue.  Adenocarcinomas of the pancreas typically excite this type of fibrous reaction (“desmoplasia”) in the surrounding tissue.  When palpated, the tumor may be extremely hard, making it virtually impossible to differentiate from chronic pancreatitis "- attribution:  Gastrointestinal Pathology for Medical II Students, VCU Department of Pathology, http://www.pathology.vcu.edu/education/gi/lab1.c.html

      • Misdiagnosis of pancreatic cancer²⁶

        • Probably the most common misdiagnosis is based on both the absence of a parenchymal pancreatic lesion and the presence of peripancreatic adenopathy. Regional lymph nodes associated with metastatic pancreatic disease are usually small or medium-sized. However, larger lymph nodes are noted with other malignancies including stomach, duodenal, esophageal tumors as well as certain colon tumors.

          • "Bulky" pancreatic lymphadenopathy may be observed in non-small cell lung cancer, lymphoma as well as with carcinomas of unknown primary pathological origin. CT imaging (thin-slice, contrast-enhanced) can identify or rule out, typically, a primary pancreatic mass. The state of atrophy (or its absence) in the pancreatic body and tail may also be diagnostically useful; atrophy is more likely seen in pancreatic adenocarcinomas associated with the head of the pancreas. Moreover, this finding is less likely in bulky, peripancreatic adenopathy and is also less likely in neuroendocrine tumors and acinar cell tumors. Pancreatic neuroendocrine tumors may be misdiagnosed as a poorly differentiated pancreatic carcinoma. Biopsy specimen stains evaluating the presence or absence of neuroendocrine markers are indicated in the presence of (1) hypervascular liver lesions, (2) normal CA 19-9 levels, or (3) patients with "well-preserved" performance status not expected based on the magnitude of tumor burden ²⁶.

• Genetic Changes in Pancreatic Cancer:

  • As noted earlier, risk factors for pancreatic cancer include type 2 diabetes as well as cigarette smoking.^{28a, 28b}  Moreover, an increase risk of pancreatic cancer appears associated within families exhibiting hereditary pancreatitis..^28c  

    • Hereditary pancreatitis, an autosomal-dominant disorder, appears associated with chromosome 7, region q35 (7q35).^28c  

      • The molecular lesion is likely a mutation in the cationic trypsinogen gene.

      • A longitudinal study of this unusual form of pancreatitis was performed in collaboration with members of the American Pancreatic Association of Pancreatology and initial criteria for participant eligibility included early age onset (<= 30 years of age), familial history, an absence of other possible causes.

      • The mean age of onset of pancreatitis symptoms was about 14 ± 12 years.

        • Of the 246 patients in the study, 8 patients developed pancreatic adenocarcinoma, several decades following symptom onset (57 ± 11 years of age). The authors estimated that the cumulative risk of pancreatic cancer in patients with hereditary pancreatitis to age 70 was about 40% and those patients with a paternal inheritance pattern exhibited a higher cumulative risk (75%).^28c  

  • A small percentage of pancreatic cancers is likely due to germline mutations.^28d

    • Utilizing the National Familial Pancreas Tumor Registry (NFPTR), investigators concluded the involvement of the major gene in pancreatic cancer development.^28e

      • This conclusion was based on segregation analysis of kindreds enrolled in the NFPTR. Furthermore, about 17% of familial clustering of pancreatic cancer appears to be caused by germ-line mutations in the BRCA2 (BReast Cancer Associated Gene 2) gene.^28f

      • Pancreatic cancer occurs in frequencies above the expected in a number of familial cancer syndromes that are associated with particular germline genetic mutations.

        • Peutz-Jeghers syndrome involves a mutation in the STK11/LKB1 chain

        • Familial pancreatitis involves mutations in the cationic trypsinogen gene, SS1PR

        • Hereditary nonpolyposis colorectal cancer exhibits mutations in DNA mismatch repair genes.

        • Familial breast cancer, another syndrome associated with increased risk of pancreatic cancer involves mutations in BRCA2.

        • Lastly, another syndrome, familial atypical multiple mole-melanoma syndrome, is associated with mutations in the p16 gene.^28f

  • Molecular Genetics:

    • Genetic alterations have been identified in pancreatic adenocarcinomas.

    • The types of genes affected in pancreatic cancer may be divided into several classes:

      •  (1) tumor suppressor genes

      • (2) oncogenes

      • (3) DNA mismatch repair genes and

      • (4) mitochondrial genes.^28g

    • →Tumor Suppressor Genes

      • BRCA2 (Breast Cancer Associated Gene 2)

        • BRCA2  is an example of a tumor-suppressor gene, which when inactivated promotes malignant transformation.^28g

        • The BRCA2 gene is inactivated in about 7% of pancreatic cancers. This inactivation is characterized both by a germline intragenic mutation and acquired somatic loss of the remaining wild-type (normally occurring) allele.^28g  

        • BRCA2 codes for a protein product which is involved in repair of breaks in double-stranded DNA. BRCA1 is a related gene which has been found to localize to sub-nuclear regions during the S and G2 cell cycle phases. ^28h

          • These regions also include a protein, Rad51, which is important in homologous recombination.

          • BRCA2, similar to BRCA1, interacts with Rad51. Rad51, BRCA1 and BRCA2 are coexpressed and development.

            • Human Rad51 is involved in repair of double-strand DNA breaks as a result of binding single-strand DNA forming a nucleoprotein filament that can "invade" a homologous duplex DNA structure.^28h  

      • p16 (MTS1/INK4A/CDKN2)

        • p16 is another tumor-suppressor gene, localized on chromosome 9p. This tumor suppressor gene is found inactivated in about 95% of pancreatic adenocarcinomas.^{28g, 28j, 28k}  

          • p16 codes for a cyclin-dependent kinase inhibitor (2A); the chain is also known as CDKN2A.

          • Cyclin-dependent kinase inhibitor 2A (p16, inhibits CDK4) (www.pdb.org)

          •  In about 40% of pancreatic adenocarcinomas, inactivation can be traced to a homologous deletion; moreover, another 40% of pancreatic adenocarcinomas are associated with the loss of one allele along with an intragenic mutation in the second. Finally, in about 15% of adenocarcinomas, the promoter region of the p16 is altered by hypermethylation.

          • The result of these alterations is the loss of the p16 gene product's ability to inhibit cell cycle promotion.

            • The gene product interferes with ATP-binding by the cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) resulting in a change in the cyclin D binding site. This change prevents CDK4 and CDK6 from phosphorylating the RB1 protein.

              • The non-phosphorylated RB1 protein does not act as a repressor of proteins which promote cell division. This failure is a failure at an important cell cycle checkpoint in most pancreatic adenocarcinomas.^28g  

      • p53

        • The TP53 gene product (also known as the p53 gene product) is inactivated at about 50%-75% of pancreatic cancer. This inactivation is characterized by a loss of one allele along with an intragenic mutation in the other one and promoter methylation.^28g,28o The p53 gene product itself activates other genes whose products affect cell cycle regulation.^28g

          • The gene encoding for the p53 gene product is localized on chromosome 17, the specific location is designated 17p13.1.

          • The encoding gene is TP53. p53 was so named because it appeared initially to have a molecular mass of 53 kilodaltons, estimated by its migration properties in a polyacrylamide gel system. Because the protein consists of a relatively higher percentage of proline amino acid residues, the gel system overestimated the molecular mass, with the being closer to 44 kilodaltons.

          • p53, RB, and p16^INK4A are considered probably the three most important tumor suppressor genes and their gene products appear interconnected biochemically. The p53 gene has been described as one of the "guardians" of the genome since it is responsive to varying types of DNA damage and its responses to stop the cell cycle or to initiate apoptosis which is programmed cell death. ^28l

          • Normally, p53 inhibits cellular proliferation by increasing cyclin-dependent kinase (CDK) inhibitor p21 levels.^28o  

            • p21 hinders retinoblastoma gene product (pRb) phosphorylation by preventing the formation of the active enzyme required for pRB phosphorylation [this prevention occurs by pRB binding to the cyclin D1/CDK4 and cyclin E/CDK2 enzyme complexes]. ^28o

            • p53 inactivation results in reduced levels of p21 inhibitor protein thus promoting cellular proliferation.^28o

          • The primary regulator of p53 is the MDM2 protein.

            • The MDM2 protein both inhibits p53 transcription and enhances p53 degradation. MDM2 activity is also controlled by an additional tumor suppressor gene p14 which is encoded within the p16^INK4A the finding of two significant tumor suppressor genes encoded by the same chromosomal locus and sharing several coding regions (exons) appears "unique" in human tumor biology.^28l

            • MDM2 is a E3 ubiquitin ligase catalyzing ubiquitination and degradation of p53^28m . The molecular details of this process can be found in reference 28m.

            •  The mdm genes were localized described in a transformed mouse BAL/c  cell line and were localized on small, acentromeric extrachromosomal nuclear bodies which were called double minutes. Therefore the MDM2 abbreviation traces back to Murine Double Minute 2 gene.^28m

        • DNA-p53 Complex (Figure author, Thomas Spletttstoesser)²⁸ⁿ

       

      • DPC4

        • DPC4 is a tumor suppressor gene found on chromosome 18q. This gene encodes for SMAD4 and appears inactivated in about 55% of pancreatic carcinomas. In 35% DPC4 gene inactivation occurs by homozygous deletion with the remaining 20% accounted for by loss of one allele along with intragenic mutation in the other allele. Inactivation of DPC4 (SMAD4) appears rather specific for pancreatic cancer. ^28g  

        • Smad proteins are involved in the transforming growth factor-β (TGF-β) signal transduction pathway.

          • TGF-β cytokines are potent growth inhibitors.

          • TGF-β super family members bind to two different serine/threonine kinase receptors (type I and type II receptors).^28p  

          • Following binding, various Smad proteins are directly or indirectly activated.^28p  

          • SMAD4 can bind directly to ‘CAGA’ DNA sequences as well as related sequences resulting in activation of transcription of target genes together with DNA-binding proteins.^28p

          • Loss of SMAD4 activity could result in RB pathway up regulation, thus promoting progression from the G1 to S phase of the cell cycle and consequent enhanced cell perforation.^28o

          • DPC4/SMAD4 Tumor Suppressor^28q

            "The Smad family of proteins mediate TGF-beta signaling from the cell membrane to the nucleus, propagating the signal by the formation of homo- and hetero-oligomers and by cooperating with other transcription factors to regulate the expression of genes. Smads are frequently targeted by tumorigenic mutations in cancer; and DPC4 is found inactivated in nearly half of all pancreatic carcinomas."28q "The Smad4/DPC4 C-terminal domain forms a trimer in the crystal, and is capable of forming hetero-hexamers with the related Smad2 protein in vitro. Mutation of residues in the Smad4 L3 loop may disrupt such hexamers and effect transmission of the TGF-beta signal to the nucleus."28q

        • SMAD4 gene (CPC4) inactivation and patient prognosis

          • Inactivation or abnormal function of tumor suppressor genes has been identified in pancreatic adenocarcinomas. However, as shown by the frequency of occurrence of these molecular pathologies, it is typically not known for a given patient which of these genetic alterations are present. The question is raised as to whether or not one or another functional deficit would have a comparable clinical impact on pancreatic cancer survivability following for example surgical resection.

          • Considering  SMAD4, but first let us review the likely biological function of smads in cell signaling.

            • Recall that the DPC4 tumor suppressor gene encodes for SMAD4 and that the tumor suppressor gene and thus the gene product SMAD4 are inactivated in about 55% of pancreatic adenocarcinomas.^28r  

              • The mechanism of inactivation is by homozygous deletion of both alleles or by intragenic mutation in one allele along with the loss of the other one.

              • SMAD4 is a protein that mediates signals from TGF-β molecules and their receptors through Smad phosphorylation.

              • Smad proteins combine with SMAD4 and the resulting complex accept the nucleus by binding to certain DNA sequences resulting in gene transcription activation. see figure below:

              •  

                "The TGF-β-SMAD4 (DPC4) Signal Transduction Pathway"^28r  

              • The functions of TGF-β and related molecules include suppression of cell proliferation and promotion of apoptosis (programmed cell death). These functions are lost following inactivation of DPC4 and the associated loss of SMAD4 protein itself.^28r  

          • The possibility that those pancreatic adenocarcinomas which exhibited loss of SMAD4 might clinically present as more aggressive, compared to those adenocarcinomas which retain SMAD4 activity has been evaluated in several studies.^28r  

            • One study determined the presence or absence of SMAD4 protein in 249 pancreatic adenocarcinomas following surgical resection (pancreaticoduodenectomy, i.e. Whipple resection). The assay involved the technique of immunohistochemistry.^28r

              • The investigators demonstrated that there was a very close correlation between DPC4/SMAD4 mutant genotype and the absence of immunohistochemical detection of SMAD4.

              • Furthermore, SMAD4 protein is lost is lost in adenocarcinomas exhibiting a wide variety of DPC4 mutations.

              • The study results suggest that patients with pancreatic adenocarcinoma exhibiting SMAD4 protein expression had longer survival (19.2 months versus 14.7 months in patients whose pancreatic cancers did not express SMAD4 protein). This finding is described in the figure below:

               

              • Survival after Pancreaticoduodenectomy (Whipple) as affected by SMAD4 Expression.^28r  

                "Survival after Whipple resection stratified for the DPC4 status of the pancreatic carcinoma. Kaplan-Meier survival curves compare the cumulative probabilty of survival after Whipple resection among tumors expressing DPC4 (SMAD4 positive) to those not expressing DPC4 (SMAD4 negative).  The P was computed using a log-rank test.28r

                 

              • The authors suggest that DPC4 gene inactivation leading to loss of SMAD4 protein apparently causes a more aggressive pancreatic adenocarcinoma as judged by clinical results.

                • The authors suggest that, because the survival advantage in patients with SMAD4-expressing pancreatic adenocarcinoma is about five added months, SMAD4 status might be useful in patient stratification with respect to clinical trials; moreover, these results suggest that new therapeutic approaches mitigating the consequence of SMAD4 loss appear reasonable in pancreatic adenocarcinoma.^28r  

          • In a separate more recent study DPC4/SMAD4 and other mutations were evaluated with respect to prognosis in 89 patients undergoing pancreaticoduodenectomy. ^28s  

            • DPC4/SMAD4 inactivation, after adjusting for lymph node status, tumor resection margin status, tumor size, and age, was associated with shorter overall survival.

            • Patients with intact (wild-type) DPC4/SMAD4 exhibited a median survival time of about 14.2 months; by comparison, in patients whose pancreatic adenocarcinoma did not express the SMAD4 protein (DPC4 gene either inactivated by intragenic mutation or by homozygous deletion) had a median survival time of 11.5 months. (See figure below)^28s  

            •  

              "Kaplan-Meier curves of survival probability for patients with and without mutation or deletion in the SMAD4 gene."^28s  

          • The authors considered other proteins associated with the TGF-β pathway, such as smad3, TGF-βR1 and TGF-βR2. The general finding was that loss of other members of the TGF-β pathway did not appear associated with a change in survival-that is, "not all of the inactivating mutations in members of the pathway have the same effect on survival".^28s  

          • Other genes associated with pancreatic adenocarcinoma were also evaluated with respect to impact on survival. These genes included CDKN2A, TP53, and KRAS (to be discussed later) and for both CDKN2A and TP53 inactivation was not associated with differences in survival. Nearly all of the adenocarcinomas exhibited a KRAS mutation so in that case comparison was not possible.^28s  

          • Blackford et al (ref 28s) suggest that the finding of a poorer prognosis in patients whose tumor exhibited DPC4 inactivation (loss of SMAD4 expression) may be due to an increased likelihood of metastasis

            • This suggestion is supported by analysis of patterns of failure ("locally destructive versus metastatic disease" as related to KRAS, TP53, and DPC4 gene status.^28t  

              • 76 patients with pancreatic adenocarcinoma underwent rapid autopsy. At autopsy, 30% of patients died with locally destructive adenocarcinoma; whereas 70% died with widespread metastases.^28t  

              • The different failure patterns, local versus metastatic, were not found related to (a) clinical stage at initial presentation, (b) treatment history, or (c) histopathologic characteristics.

              • On the other hand, DPC4 immunolabeling was highly correlated with the metastatic pattern.^28t   

              • One specific finding: 2 (representing 22%) of 9 locally advanced carcinomas with no apparent metastatic disease at autopsy exhibited DPC4 loss. However, 16 (78%) of 22 carcinomas with "100s to 1000s of metastases" exhibited DPC4 loss. A similar but less dramatic finding was noted with TP53 mutations.^28t  

              • The authors of this detailed histopathological-genetic analysis suggested three primary clinical implications:

                • →1. Not all pancreatic cancer patients die of widespread metastatic disease.

                • →2. A pancreatic carcinoma' s genetic status could be used to predict widespread metastatic failure.

                • →3 Advanced  pancreatic cancers are more likely to exhibit a high grade histologic features compared to early-stage disease.^28t